The 12-lead ECG shows sequential atrial and
ventricular pacing (Figure 1A).
A tracing, obtained simultaneously during pacemaker interrogation,
disclosed pacemaker functioning as VDD mode (Figure 1B). The careful examination
of this pacemaker tracing showed that there is a pacing stimulus before
each P wave (compatible with DDD mode). This paradox can only be
explained by displacement of the temporary pacing lead to right atrium
and right atrial stimulation by temporary pacemaker. In this setting,
each temporary pacemaker-induced atrial depolarization is tracked by
the right atrial lead of the permanent pacemaker as intrinsic P wave.
Fluoroscopic study confirmed this explanation (Figure 2). The displaced temporary
pacing lead was seen near the lateral right atrial wall. Temporary
pacemaker lead had been inserted before replacement of permanent
pacemaker.